Evaluate each algebraic expression at the indicated values of the variables.

1. 4x - x2 at x = - 2

2. 10 - 6(4 - x)2 at x = -1

3. 10xy - 4(x - y)2 at x = 5 and y = -2

4. 3x2 - 4y2 - 2xy at x = 3 and y = - 4